Question

I have a NSArray of ‘generic Objects’ which contain the following properties

-name
-id
-type (question, topic or user)

How can I sort this array of generic object based on the generic object’s type? E.g. I want to display all generic objects of type ‘topic’ on the top, followed by ‘users’ than ‘questions’

Answer 1

You’ll need to define a custom sorting function, then pass it to an NSArray method that allows custom sorting. For example, using sortedArrayUsingFunction:context:, you might write (assuming your types are NSString instances):

NSInteger customSort(id obj1, id obj2, void *context) {
    NSString * type1 = [obj1 type];
    NSString * type2 = [obj2 type];

    NSArray * order = [NSArray arrayWithObjects:@"topic", @"users", @"questions", nil];

    if([type1 isEqualToString:type2]) {
        return NSOrderedSame; // same type
    } else if([order indexOfObject:type1] < [order indexOfObject:type2]) {
        return NSOrderedDescending; // the first type is preferred
    } else {
        return NSOrderedAscending; // the second type is preferred
    }   
}   

// later...

NSArray * sortedArray = [myGenericArray sortedArrayUsingFunction:customSort
                                                         context:NULL];

If your types aren’t NSStrings, then just adapt the function as needed – you could replace the strings in the order array with your actual objects, or (if your types are part of an enumeration) do direct comparison and eliminate the order array entirely.